Abstract: 4-coumarate:coenzyme A ligase catalyzes the forming of the corresponding CoA thioesters of cinnamate and its hydroxylated derivatives in vascular plants.The enzymatic properties of the recombinant 4CL1 from Populus tomentosa were primarily characterized.Assay of thermostability over a range of temperatures showed that the enzyme displayed relative high activity at 40℃.However,when the temperature exceeded 35℃,it became unstable quickly.An investigation on the thermotolerance of recombinant Pt4CL1 was done by applying 10% glycerol.Results displayed that it could help improving the thermostablility of Pt4CL1 at 35℃.pH stability analysis revealed that Pt4CL1 was comparatively stable at pH 3.0 to 8.0,and the optimum pH of enzyme reaction was 8.0.However,it was unstable enough when pH was over 8.0.Magnesium was the best activator for Pt4CL1,and EDTA (ethylenediamine tetracetic acid) inhibited Pt4CL1 activity markedly as a result of EDTA chelating the divalent metal cofactor.It was most active when tris-buffer was 0.2 mol/L.The substrate preference analysis shows that Pt4CL1 4-coumarate is the fittest substrate among the five different ones.